Modified the mechanism that validated the Display being a 'sane' object according to Elliot's suggestion
Modified the mechanism that validated the Display being a 'sane' object according to Elliot's suggestion

OpenSmalltalk/vm,OpenSmalltalk/vm,bencoman/pharo-vm,OpenSmalltalk/vm,OpenSmalltalk/vm,OpenSmalltalk/vm,bencoman/pharo-vm,peteruhnak/pharo-vm,OpenSmalltalk/vm,timfel/squeakvm,bencoman/pharo-vm,timfel/squeakvm,peteruhnak/pharo-vm,OpenSmalltalk/vm,bencoman/pharo-vm,bencoman/pharo-vm,peteruhnak/pharo-vm,bencoman/pharo-vm,peteruhnak/pharo-vm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,timfel/squeakvm,timfel/squeakvm,peteruhnak/pharo-vm,peteruhnak/pharo-vm,bencoman/pharo-vm,peteruhnak/pharo-vm,bencoman/pharo-vm,peteruhnak/pharo-vm,timfel/squeakvm,bencoman/pharo-vm